Method of and apparatus for rapidly abrading metal workpieces

ABSTRACT

The surface of a workpiece is rapidly abraded by a fast moving abrasive belt trained over a contract drum and against which the workpiece is forcefully engaged. The workpiece is carried on a work supprt that rotates on an axis near and transverse to that of the drum and which intersects the drum intermediate its ends. The work support has feeding and retracting motion substantially parallel to its axis, and feed force is applied to it in one embodiment of the invention by an elastic biasing medium from which stored mechanical energy is released during feed; in another, the feed force is produced by controlled rotation of jack screws, and in still another embodiment of the invention, the feed force is provided by hydraulic pressure governed by a spring-biased pressure-responsive control valve. Feed rate control is also incorporated in the machine to adapt it to use on interrupted surfaces and to different materials.

United States Patent 1191 Grivna et a1.

1451 June 18, 1974 METHOD OF AND APPARATUS FOR RAPIDLY ABRADING METAL WORKPIECES Related US. Application Data [63] Continuation of Ser. No. 242,111, April 7, 1972,

abandoned, which is a continuation-impart of Ser. No. 181,474, Sept. 17, 1971, abandoned, which is a continuation-in-part of Ser. No. 38,431, May 18, 1970, abandoned.

[52] US. Cl..... 51/145 T, 51/165.9, 51/216 ND, 51/328 [51] Int. Cl B24b 21/12, B24b 21/18 [58] Field of Search... 51/145 R, 145 T, 328, 165.9, 51/131, 132,134,216 T, 216 ND, 135 R, 97

R, 135 ET, 108 R, 105 R, 147; 241/231; 173/158 [56] References Cited UNITED STATES PATENTS 537,274 4/1895 Carroll 51/145 R 2,320,874 6/1943 Lehmann 173/158 x 8/1946 Wharton 51/145 T 2,901,871 9/1959 Kluge 51/145 R 3,099,406 7/1963 Kautz ...'24l/23l X 3,154,896 11/1964 Olton 51/328 3,369,328 2/1968 Freerks 1 51/l65.9 X 3,668,814 6/1972 Freerks 51/145 R X 3,710,516 1/1973 Kelly 51/283 Primary Examiner-Donald G. Kelly [5 7] ABSTRACT The surface of a workpiece is rapidly abraded by a fast moving abrasive belt trained over a contract drum and against which the workpiece is forcefully engaged. The workpiece is carried on a work supprt that rotates on an axis near and transverse to that of the drum and which intersects the drum intermediate its ends. The work support has feeding and retracting motion substantially parallel to its axis, and feed force is applied to it in one embodiment of the invention by an elastic biasing medium from which stored mechanical energy is released during feed; in another, the feed force is produced by controlled rotation of jack screws, and in still another embodiment of the invention, the feed force is provided by hydraulic pressure governed by a spring-biased pressure-responsive control valve. Feed rate control is also incorporated in the machine to adapt it to use on interrupted surfaces and to different materials. 1

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1. The method of machining a surface of a workpiece whether interrupted or not, to a predetermined level by grinding the same with an endless abrasive belt having a stretch thereof supported against the thrust of the workpiece thereon by a backup member which engages the back side of the belt, which method comprises: A. fixing the workpiece to a work supporting member that is rotatable about an axis that passes substantially perpendicularly through the zone of contact between the workpiece and the abrasive belt, with said workpiece surface facing the backup member-supported abrasive belt; B. rotating the work supporting member about said axis; C. while the work suPporting member and the workpiece thereon are rotating, applying to one of said members a feed force that yields upon resistance thereto in excess of a predetermined magnitude, to thereby effect relative work feeding motion between said members in the direction and in a manner to produce grinding engagement under substantially constant pressure between the workpiece and the backup member-supported abrasive belt; and D. so controlling the rate of said relative work feeding motion between said members that the rate of said relative motion is unaffected by changes in the nature of the contact between the workpiece and the abrasive belt.
 2. a turret having means to grip the workpiece, and
 2. means comprising part of said yieldable force applying means for cushioning sudden increases in the feed force manifested at the engagement between the workpiece and the abrasive belt and resulting from transient high spots in the workpiece surface and/or hard spots therein.
 2. bearing means mounting the work support on the hinged arm for rotation about an axis normal to the axis about which the arm swings, and
 2. means mounting the hinged arm for swinging motion towards and from the contact drum about a hinge axis that is generally parallel with the axis of the contact drum; C. mounting structure for the contact drum and the mounting means for said hinged arm, said mounting structure providing for
 2. relative work feeding motion between the work support and the contact drum towards one another along a path substantially parallel to the axis of the work support to effect engagement between a workpiece on the work support and the contact drum-supported abrasive belt along a narrow work zone which is substantially intersected by a plane that contains the axis of the contact drum; and
 2. a turret having means to grip the workpiece, and
 2. means hingedly Mounting said arm for swinging motion towards and from the contact drum member about a hinge axis that is generally parallel with the axis of the contact drum member; said mounting structure further providing for tiltable relative adjustment between said hinge axis and the axis of the contact drum member in directions parallel to said plane that substantially intersects the work zone, to enable said hinge axis and the axis of the contact drum member to be brought into true parallelism or to be inclined to one another in said directions, and means for effecting such tilting adjustment.
 2. wherein the work supporting member has a work supporting surface to which a workpiece may be secured, and further characterized by: A. a supporting arm for the work supporting member; B. means rotatably mounting the work supporting member on said arm for rotation about an axis perpendicular to its work supporting surface; C. hinge means mounting said supporting arm for swinging motion about an axis parallel to that of the contact drum member between a lowered position in which the work supporting surface is substantially horizontal, and an upright position in which the axis of the work supporting member perpendicularly intersects the axis of the contact drum member medially of its ends; D. wherein said force producing means reacts between said hinged supporting arm and said relatively fixed part of the machine when the arm is in its upright position to feed a workpiece on the work supporting member against the contact drum supported abrasive belt means; and E. drive means for rotating the work supporting member about its axis while a workpiece thereon is being fed against the abrasive belt means.
 2. means to secure said frame member in an upright position, and further characterized in that: said force producing means for imparting work feeding motion to the rotatable work supporting member comprises fluid pressure responsive means reacting between said hinged frame member and said hinged arm.
 2. means for compressing said closed air chamber to thereby store a predetermined amount of mechanical energy in said chamber, the release of which imparts work feeding motion to the work support.
 2. wherein said endless abrasive belt means has areas of different grit size to provide for rough abrading and finish abrading,
 2. the axis about which the work support turns being generally parallel to the turntable axis and spaced therefrom by a distance substantially equal to the spacing between said turntable axis and the axis of the contact drum, so that by rotation of the turntable the rotary work support can be moved between a working position in which its axis of rotation is near the axis of the contact drum and a loading and unloading position in which it is spaced to one side of the contact drum.
 2. relative work feeding motion between the work support and the contact drum towards one another along a path substantially parallel to the axis of the work support to effect engagement between a workpiece on the work support and the contact drum-supported abrasive belt along a narrow work zone which is substantially intersected by a plane that contains the axis of the contact drum; D. a closed air chamber, certain walls of which are resiliently deformable and in which energy can be stored by contraction of the air chamber, said air chamber being interposed between the work support and a rigid support so that release of energy stored therein by expansion of said closed air chamber effects relative work feeding motion between said work support and the contact drum; E. means for contracting said air chamber to thereby store energy therein; and F. means for rotating the work support about its axis so that a workpiece attached to the work support by such rotation will have the entire area of its surface which is to be abraded operatively engaged with the abrasive belt.
 2. bearing means mounting the work support on the hinged arm for rotation about an axis which in the operative position of the work support passes transversely through the contact drum medially of its ends and near the axis of the contact drum; G. means for moving the frame structure and the work support thereon to bring the same to a position in which a workpiece on the work support is spaced a predetermined distance from the contact drum, determined by the dimensions of the workpiece to be ground; H. elastic biasing means interposed between the hinged arm and the frame structure, in which mechanical energy can be stored by relative movement towards one another between the hinged arm and the frame structure, the release of such energy producing work feeding motion of the work support whereby a workpiece attached to the work support is fed against the drum-supported abrasive belt; I. power means operable to effect such relative movement between the hinged arm and the frame structure; and J. drive means on the hinged arm drivingly connected with the rotatable work support to rotate the latter.
 2. The method of claim 1, wherein said relative work feeding motion between said members is produced by fluid pressure cylinder means having a head end into which fluid under pressure is fed to produce said relative work feeding motion and a rod end from which fluid flows during said relative work feeding motion.
 3. The method of claim 2, wherein the control of the rate of said relative work feeding motion is achieved by regulating the flow of the pressure fluid out of the rod end of said hydraulic cylinder means.
 3. bearing means rotatably connecting the turret with said hinged arm; and C. wherein said force producing means reacts between said hinged arm and said frame structure.
 3. tiltable relative adjustment between the hinge axis of said hinged arm and the axis of the contact drum in directions parallel to said plane that substantially intersects the work zone, to enable said hinge axis and the axis of the contact drum to be brought into true parallelism or to be inclined to one another in said directions; D. means for effecting such tilting adjustment; E. yieldable force applying means arranged to effect relative work feeding motion between said work support and the contact drum, said yieldable feed force applying means comprising a hydraulic pressure responsive device connected with a pressure source; and F. means for cushioning sudden increases in the feed force manifested at the engagement between the workpiece and the abrasive belt resulting from transient high spots in the workpiece surface and/or hard spots therein, said cushioning means comprising control valve means which is sensitive to changes in the force manifested at the engagement between the workpiece and the abrasive belt and operable to govern connection of the hydraulic pressure responsive device with its pressure source.
 3. means for bringing the rotatable work support into cooperative relation with all of said different grit size abrasive belt means, so that a workpiece can be successively abraded by the different grit size belt means without removing the workpiece from the rotatable work support; G. force applying means interposed between the hinged arm and said frame structure for moving the hinged arm towards the contact drum means to thereby feed the workpiece attached to the work support against one of said abrasive belt means; and H. drive means on the hinged arm drivingly connected with the rotatable work support to rotate the latter.
 3. bearing means rotatably connecting the turret with said hinged arm; and C. means for imparting work feeding motion to the work support and exerting a substantially large feed force thereon characterized by
 3. wherein said machine has a main frame in which the contact drum member is rotatably mounted, and further characterized by: A. frame structure mounted in said main frame for translation towards and from the contact drum member in directions radial thereto; B. wherein the work supporting member is rotatably mounted on said frame structure by means of an arm hingedly connected with the frame structure for swinging movement in directions laterally toward and from the contact drum member; C. bearing means mounting the work supporting member on the hinged arm for rotation about an axis normal to the axis about which the arm swings; D. means for bringing the rotatable work supporting member into cooperative relation with all of said different grit size areas of the abrasive belt means, so that a workpiece on the work supporting member can be successively abraded by the different grit size areas of the abrasive belt means without removing the workpiece from the rotatable work supporting member; E. drive means on the hinged arm drivingly connected with the rotatable work supporting member to rotate the latter; and F. wherein said force producing means reacts between the hinged arm and said frame structure to move the hinged arm towards the contact drum member and thereby feed the workpiece on the work supporting member against one of said different grit size areas of the abrasive belt means.
 4. The method of claim 2, wherein the control of the rate of said relative work feeding motion is achieved by regulating relative rotation between a screw and nut connection, arranged to restrain the motion produced by said fluid pressure cylinder means.
 5. The method of claim 1, wherein the backup member is fixed, and wherein said relative motion between said members is obtained by moving the work supporting member towards the backup member.
 6. The method of claim 2, wherein the backup member is fixed, and wherein said hydraulic cylinder means reacts between the work supporting member and a point fixed with respect to the backup member.
 7. The method of claim 1, wherein said backup member is a contact drum member and wherein the axis about which the work supporting member rotates is substantially radial to the axis of the contact drum.
 8. The method of claim 7, wherein the axis about which the contact drum member rotates is fixed, and wherein said relative motion between said members is obtained by moving the work supporting member towards the contact drum member.
 9. The method of claim 8, wherein said movement of the work supporting member towards the contact drum member is produced by steadily mechanically advancing a rigid member towards the side of the contact drum member at a uniform predetermined rate, and imparting the motion of the advancing rigid member to the work supporting member through a yieldable motion transmitting connection which does not yield as long as the feed force between the workpiece and the drum-supported abrasive belt remains below a predetermined maximum.
 10. The method of claim 9, wherein the advance of said rigid member towards the contact drum member is effected by relative rotation between a screw and nut, and wherein the control of the rate at which the workpiece is fed against the abrasive belt is achieved by regulating the drive by which relative rotation between the screw and nut is produced.
 11. The method of claim 1, further characterized by: with the workpiece in grinding engagement with the backup member supported abrasive belt, oscillating the work supporting member about an axis parallel to the axis about which the workpiece rotates, and so located with respect to the backup member that the arc defined by the oscillatory motion of the work supporting member lies in a plane that is substantially parallel to the zone of contact between the abrasive belt and the workpiece.
 12. The method of machining either an uninterrupted substantially flat surface of a workpiece or a plurality of spaced apart substantially falt surfaces thereof to a desired predetermined level by means of an endless abrasive belt trained over a rotatable contact drum, which method comprises: A. providing a rotatable work support to which the wOrkpiece is secured; B. providing a yieldable feed force; C. by means of said yieldable feed force, effecting relative work feeding motion between the workpiece and the drum-supported abrasive belt; D. so governing said yieldable feed force that at no time will it exceed a predetermined magnitude but will yield to any transient increase in load; E. while the workpiece is in contact with the drum-supported abrasive belt, effecting rotary motion of the workpiece about an axis which is normal to the substantially flat surface of the workpiece and which passes transversely through the contact drum, to bring the entire area of the surface or surfaces of the workpiece being machined into operative engagement with the abrasive belt; F. so controlling the rate at which said yieldable feed force effects relative work feeding motion, that regardless of discontinuity in contact between the workpiece and the abrasive belt, the rate of said relative work feeding motion remains substantially constant; and G. when the desired level to which said workpiece surface or surfaces is to be machined has been reached, arresting the relative work feeding motion.
 13. The method of machining a surface of a workpiece whether interrupted or not, to a predetermined level by grinding the same with an endless abrasive belt trained about a rotating contact drum which supports the abrasive belt against the thrust of the workpiece thereon, which method comprises: A. fixing the workpiece to a work support that is rotatable about an axis substantially radial to that of the contact drum and passes through the drum, with said workpiece surface facing the drum-supported abrasive belt; B. rotating the work support about said substantially radial axis; C. while the work support and the workpiece thereon are rotating, effecting relative work feeding motion between the work support and the contact drum in the direction and in a manner to produce grinding engagement under substantially high pressure between the workpiece and the drum-supported abrasive belt; and D. with the workpiece in grinding engagement with the abrasive belt, oscillating the work support about an axis parallel to the axis about which the workpiece rotates, and so located with respect to the contact drum that the arc defined by the oscillatory motion of the work support is substantially parallel to the axis of the drum.
 14. The method of machining a substantially flat surface of a workpiece to a desired predetermined level by means of an endless abrasive belt trained over a contact drum constrained to rotate about a fixed axis, which method includes rotating the workpiece while in contact with the abrasive surface, about an axis normal to the axis of the contact drum, to bring the entire area of the surface of the workpiece being machined into operative engagement with the abrasive surface and which method is characterized by: A. effecting a feed force between the workpiece and the contact drum-supported abrasive belt by disposing a closed chamber having resiliently deformable walls, and in which mechanical energy can be stored, in such relation to the workpiece and the contact drum that release of mechanical energy stored in said chamber produces work performing engagement between the workpiece and the contact drum-supported abrasive belt; B. contracting said chamber to store energy therein; C. releasing energy stored in said chamber by allowing it to expand to thereby yieldingly effect the desired feed force; and D. when the level to which the workpiece surface is to be machined is tangent to the contact drum-supported abrasive belt, arresting further expansion of the closed air chamber.
 15. The method of machining a substantially flat surface of a workpiece to a desired predetermined level by grinding the same with an endless abrasive belt trained over a rotating contact drum which supports the abrasive belt against the thrust of The workpiece thereon, which method comprises: A. providing a compressible elastic walled chamber in which mechanical energy can be stored; B. compressing the elastic walled chamber to store a predetermined amount of mechanical energy therein; C. by the release of said mechanical energy in the elastic walled chamber, effecting grinding engagement and relative work feeding motion between the workpiece and the drum-supported abrasive belt; D. with the workpiece in grinding engagement with the drum-supported abrasive belt, rotating the workpiece about an axis which is normal to said substantially flat surface of the workpiece and which passes transversely through the contact drum, to bring the entire area of said surface into operative engagement with the drum-supported abrasive belt; and E. when the level to which said workpiece surface is to be ground is tangent to the curved surface of the drum-supported abrasive belt, arresting said relative work feeding motion between the workpiece and the drum-supported abrasive belt.
 16. The method of claim 15, wherein the compression of the compressible elastic walled chamber is effected by applying hydraulic pressure upon a part connected therewith.
 17. The method of claim 16, further characterized by fully releasing said hydraulic pressure to allow the energy stored in the compressible elastic walled chamber to effect unrestricted relative work feeding motion between the workpiece and the contact drum-supported abrasive belt.
 18. The method of claim 1, further characterized in that successive workpieces are rotated in opposite directions.
 19. A surface abrading machine of the type comprising endless abrasive belt means having a stretch thereof supported by a backup member engaging the back side of the belt means, a work supporting member upon which a workpiece is held to be abraded by said abrasive belt means and which is rotatable on an axis that substantially perpendicularly intersects the zone of contact between the workpiece and the belt means, one of said members being movable toward and from the other to provide for engagement and disengagement between the workpiece and the abrasive belt means for relative feeding motion therebetween as abrasion takes place, said machine being characterized by: A. power drive means arranged to react between said one member and a relatively fixed part of the machine to effect relative feeding motion of said one member toward the other to thereby bring out engagement between the surfaces of the workpiece and the abrasive belt means to cause abrasion of the workpiece; and B. means unaffected by discontinuity in contact between the workpiece and the abrasive belt means resulting from interruption in the workpiece surface being ground, for controlling the rate at which said power drive means effects said relative feeding motion.
 20. The surface abrading machine of claim 19, wherein said power drive means comprises a fluid pressure responsive device connected with a source of fluid pressure, and wherein said means for controlling the rate at which said relative feeding motion occurs comprises a flow control valve connected with said fluid pressure responsive device.
 21. The surface abrading machine of claim 19, wherein said power drive means comprises a fluid pressure responsive device connected with a source of fluid pressure, and wherein said means for controlling the rate at which said relative feeding motion occurs comprises a screw and nut connection between said one member and said relatively fixed part of the machine and arranged to resist the force produced by the fluid pressure responsive device.
 22. The surface abrading machine of claim 19, wherein said power drive means comprises a screw and nut connection between said one member and said relatively fixed part of the machine, wherein said means for controlling the rate at which said relative feeding motion occurs includes power actuated means for regUlating relative rotation between the screw and nut; and further characterized by yieldable means through which the force produced by said power drive means is imparted to said one member.
 23. The surface abrading machine of claim 19, further characterized by: means providing yieldability in the motion producing effect of the force producing means on said one member, to thereby cushion sudden increases in the feed force manifested at the engagement between the workpiece and the abrasive belt means and resulting from transient high spots in the workpiece surface and/or hard spots therein.
 24. The surface abrading machine of claim 23, wherein said means for providing yieldability in the motion producing effect of said force producing means comprises: a closed air chamber having resiliently deformable wall means and containing air under pressure, and through which said force producing means acts to effect said relative motion.
 25. The abrading machine of claim 23, wherein said force producing means comprises: a fluid pressure responsive device connected with a pressure source; and wherein said means for providing yieldability in the motion producing effect of said force producing means comprises control valve means which is sensitive to changes in the force manifested at the engagement between the workpiece and the abrasive belt means and operable to govern connection of the fluid pressure responsive device with its pressure source.
 26. The abrading machine of claim 19, wherein said backup member is a rotatable contact drum member, and further characterized by: A. a frame structure which maintains a fixed relationship to the axis of the contact drum member during at least the final portion of the operation performed by the machine; B. wherein said work supporting member comprises
 27. The abrading machine of claim 19, wherein said backup member is a rotatable contact drum member, and further characterized by: A. mounting structure for the contact drum member and the rotatable work supporting member, by which said members are mounted in the relationship set forth in claim 19, and wherein by virtue of said relationship, the work performing engagement between the workpiece and the drum supported abrasive belt means extends along a narrow zone which is substantially intersected by a plane that contains the axis of the contact drum member; B. wherein said force producing means is yieldable and comprises a hydraulic pressure responsive device connected with a pressure source; and further characterized by C. means for cushioning sudden increases in the feed force manifested at the engagement between the workpiece and the drum supported abrasive belt means resulting from transient high spots in the workpiece surface and/or hard spots therein, said cushioning means comprising control valve means which is sensitive to the force manifested by the engagement between the workpiece and the abrasive belt means and operable to govern connection of the hydraulic pressure responsive device with its pressure source.
 28. The abrading machine of claim 27, further characterized by: means for arresting relative feeding motion between the contact drum member and the work supporting member when a workpiece on the work supporting member has been abraded to a predetermined level.
 29. The abrading machine of claim 27, further characterized by: the work supporting member comprising
 30. The abrading machine of claim 27, wherein the mounting structure further comprises means for effecting tilting adjustment of the contact drum member.
 31. The abrading machine of claim 19, wherein said backup member is a rotatable contact drum member, and further characterized in that
 32. The abrading machine of claim 31, wherein said hinge means comprises
 33. The abrading machine of claim 32, further characterized by: A. a carriage slidably mounted on the main frame of the machine for translation perpendicularly towards and from the contact drum member; B. wherein the common hinge axis of said hinged arm and hinged frame member is fixed with respect to said carriage so that translation of the carriage provides for adjustment of the distance between the work receiving surface of the rotatable work supporting member and the contact drum member to adapt the machine to different sized work; and C. means for effecting translation of the carriage; and further characterized in that said means for securing said hinged frame member in its upright position comprises latch means on said carriage engageable with said hinged frame member.
 34. The abrading machine of claim 19, wherein
 35. The abrading machine of claim 34, wherein said means for bringing the rotatable work supporting means into cooperative relation with said different grit size areas of the abrasive belt means does so individually and successively, so that a workpiece can be successively abraded by the different grit size areas of the abrasive belt means without removing it from the rotatable work support.
 36. The abrading machine of claim 35, wherein the different grit size areas of the abrasive belt means are supported on and driven by a single contact drum member, and wherein said means for bringing the work supporting member into cooperative relation individually with the different grit size areas of the abrasive belt means provides for relative displacement between the work supporting member and the contact drum member along a path generally parallel to the axis of the contact drum member.
 37. The abrading machine of claim 34, wherein the different grit size areas of the abrasive belt means are supported by a plurality of contact drums that are disposed in tandem spaced parallel relationship, and wherein said means for bringing the work supporting member into cooperative relation individually with the different grit size areas of the abrasive belt means provides for relative displacement between the work supporting member and said plurality of contact drums along a path generally normal to the axes of the contact drums.
 38. The abrading machine of claim 19, wherein said backup member is a rotatable contact drum means, further characterized by: A. a turntable mounted to rotate about a fixed axis; B. wherein said contact drum means comprises a plurality of contact drums rotatable about fixed axes normal to the axis of the turntable with their peripheries tangent to a single plane spaced from and generally parallel to the turntable, said contact drums being equispaced from the axis of the turntable; C. an abrasive belt being trained over each contact drum, said belts being of different grit size; D. wherein said work supporting member comprises a plurality of rotatable work supports, each adapted to have a workpiece attached thereto; E. means mounting each of the rotatable work supports on the turntable with their axes parallel to that of the turntable and equispaced therefrom a distance such that upon indexed rotation of the turntable the work supports are successively brought into cooperative relation with the contact drums, so that a workpiece on a rotatable work support can be successively fed against the different abrasive belts without removing it from the work support to which it is attached, said means for mounting the work supports on the turntable comprising arms hinged at one end to the turntable and having the work supports rotatably mOunted on the other ends thereof; F. wherein said force producing means comprises yieldable biasing means reacting between each arm and the turntable to feed the workpiece on its respective work support successively against each of the abrasive belts with a force not exceeding a predetermined magnitude; and G. power means for rotating the work supports while the workpieces thereon are being fed against the abrasive belts.
 39. In a machine for abrading the surface of a workpiece to a predetermined level by maintaining the workpiece engaged under high force against the active surface of an endless abrasive belt trained over a contact drum rotating on a fixed axis, work feeding means for said machine comprising: A. a frame structure which maintains a fixed relationship to the contact drum axis during at least the final portion of the abrading operation performed by the machine; B. a work support by which the workpiece is held; C. means mounting the work support on the frame structure for work feeding motion relative to the frame structure in a direction substantially radial to the drum; and D. means for imparting work feeding motion to the work support, characterized by
 40. The structure of claim 39, further characterized by motion limiting means operatively connected with the movable work support and the frame structure for positively limiting the work feeding motion imparted to the work support by the release of energy stored in said closed air chamber, to provide for termination of feeding motion when the workpiece has been abraded to the predetermined level.
 41. The structure of claim 39, wherein the work support is a rotatable turret; and the means mounting the work support comprises: A. an arm hingedly connected with the frame structure for movement with respect thereto about an axis substantially parallel with the axis of the contact drum; and B. bearing means rotatably connecting the turret with said hinged arm.
 42. The structure of claim 41, further characterized by drive means on said hinged arm operatively connected with the turret to impart rotation thereto.
 43. The structure of claim 39, wherein the means for compressing said closed air chamber comprises: positive motion producing means operatively connected with said frame structure to move the same a distance towards the axis of the contact drum, which distance is determined by the depth of material to be removed in abrading the workpiece.
 44. The structure of claim 39, wherein the means for compressing said closed air chamber comprises: motion producing power means connected with said frame structure and said hinged arm and arranged to move the latter away from the drum axis and thereby compress said air chamber.
 45. An abrading machine comprising: A. a main frame; B. a contact drum mounted in the frame for rotation about a fixed axis; C. an endless abrasive belt trained over the contact drum; D. a frame structure mounted in the main frame for movement towards and from the contact drum in directions radial thereto; E. a rotatable work support adapted to have a workpiece to be ground attached thereto; F. means mounting the rotatable work support on the frame structure for movement to and from an operative position engaging a workpiece thereon with the drum supported abrasive belt, said mounting means comprising
 46. The abrading machine of claim 45, wherein the power means is connected with said means for translating the frame structure and effects relative motion between said hinged arm and the frame structure by effecting motion of the frame structure toward the drum axis while a workpiece on the work support is engaged with the belt.
 47. The abrading machine of claim 45, wherein said power means comprises a motion producing motor reacting between the hinged arm and the frame structure.
 48. The abrading machine of claim 47, wherein said motion producing motor comprises a hydraulic cylinder and piston, further characterized by: A. said hydraulic cylinder and piston being so arranged that pressure fluid fed to the cylinder draws the hinged arm towards the frame structure; and B. further characterized by means for metering flow of such pressure fluid from the cylinder to regulate the rate at which energy released from the elastic biasing means effects engagement of the workpiece with the drum-supported abrasive belt.
 49. The abrading machine of claim 45, further characterized in that said frame structure comprises: A. a non-rotatable unit constrained to translation; and B. a turntable rotatably mounted on said unit for rotation about an axis normal to the axis of the contact drum, but spaced therefrom,
 50. In an abrading machine wherein work to be ground is forced against the active surface of an endless abrasive belt trained over a contact drum rotating on a fixed axis, work feeding means for said machine comprising: A. a turntable mounted to rotate about an axis normal to, but spaced to one side of, the axis of the contact drum, and for translation along its own axis of rotation; B. an arm hingedly mounted on the turntable for swinging movement from and toward the contact drum axis, about an axis substantially parallel with that of the contact drum, by which movement the arm is carried to and from a retracted position; C. a work carrying turret rotatably mounted on said arm and having means by which a workpiece amy be attached thereto, rotation of the turntable enabling the turret to be moved between an operative work performing position in juxtaposition to the contact drum and a loading and unloading station spaced from thE contact drum; D. means for effecting translation of the turntable to a position determined by the dimensions of a workpiece attached to the turret and at which positon swinging movement of the hinged arm away from its retracted position feeds the workpiece carried by the turret against the drum-supported abrasive belt; E. elastic biasing means reacting between the hinged arm and the turntable and in which mechanical energy is stored in consequence of hinged movement of the arm toward its retracted position, such stored energy, when released, being available to move the arm away from its retracted position; and F. means for rotating the turret to bring the entire area of the workpiece surface being ground into operative engagement with the drum-supported abrasive belt.
 51. The abrading machine of claim 50 wherein the elastic biasing means is interposed between the hinged arm and the turntable; and wherein the axis about which said hinged arm swings is intersected by the axis of the turntable so that said hinged arm, the turret thereon and the elastic biasing means are all located at one side of the turntable axis; and wherein said hinged arm, the work carrying turret thereon and the elastic biasing means are duplicated at the diametrically opposite side of the turntable, so that 180* of rotation of the turntable interchanges the work carrying turrets which are respectively at the operative position and at the loading and unloading station.
 52. The abrading machine of claim 51, further characterized in that the means for rotating the turrets drives them in opposite directions.
 53. An abrading machine having an endless abrasive belt as its work performing element and comprising: A. a contact drum rotatable about its axis and over which the abrasive belt is trained; B. a rotatable work support adapted to have a workpiece attached thereto; C. mounting structure for the contact drum and the rotatable work support, said mounting structure providing for
 54. The abrading machine of claim 53, further characterized by: means for limiting expansion of said closed air chamber to thereby terminate relative feeding motion between the contact drum and the work support when a workpiece on the work support has been abraded to a predetermined level.
 55. The abrading machine of claim 53, further characterized by: A. the work support comprising a turret rotatably mounted on a hinged arm; B. said mounting structure comprising means hingedly mounting said arm for swinging motion towards and from the contact drum about a hinge axis that is generally parallel with the axis of thE contact drum; C. said mounting structure further providing for tiltable relative adjustment between said hinge axis and the axis of the contact drum in directions parallel to said plane that substantiallly intersects the work zone, to enable said hinge axis and the axis of the contact drum to be brought into true parallelism or to be inclined to one another in said directions; and D. means for effecting such tilting adjustment.
 56. The abrading machine of claim 54, wherein the mounting structure provides for tilting adjustment of the contact drum.
 57. In a machine for abrading the surface of a workpiece to a predetermined level by maintaining the workpiece engaged under high force against the active surface of an endless abrasive belt trained over a contact drum rotating on a fixed axis, work feeding means for said machine comprising: A. a frame structure which maintains a fixed relationship to the contact drum axis during at least the final portion of the abrading operation performed by the machine; B. a work support by which the workpiece is held, said work support comprising
 58. The structure of claim 57, wherein said yieldable force applying means comprises a hydraulic pressure responsive device connected with a source of hydraulic pressure and a pressure regulating valve responsive to the pressure exerted by said hydraulic pressure responsive device to govern the magnitude of the feed force delivered by said yieldable force applying means.
 59. An abrading machine comprising: A. a main frame; B. contact drum means rotatably mounted in the main frame; C. endless abrasive belt means of different grit size trained over the contact drum means, to provide for rough abrading and finish abrading; D. a frame structure mounted in the main frame for translation towards and from the contact drum means in directions radial thereto; E. a rotatable work support adapted to have a workpiece to be abraded attached thereto; F. means mounting the rotatable work support on the frame structure comprising
 60. An abrading machine having an endless abrasive belt as its work performing element and comprisiNg: A. a contact drum rotatable about its axis and over which the abrasive belt is trained; B. a rotatable work support adapted to have a workpiece attached thereto and comprising
 61. The abrading machine of claim 60, further characterized by: means for arresting relative feeding motion between the contact drum and the work support when a workpiece on the work support has been abraded to a predetermined level.
 62. The abrading machine of claim 60, wherein the mounting structure further comprises means for effecting tilting adjustment of the contact drum.
 63. An abrading machine having a main frame and an endless abrasive belt trained over a horizontally oriented contact drum as its work performing element, and comprising: A. a work support having a work supporting surface to which a workpiece may be secured; B. a supporting arm for the work support; C. means rotatably mounting the work support on its supporting arm for rotation about an axis perpendicular to its work supporting surface; D. hinge means mounting said supporting arm for swinging motion about an axis parallel to that of the contact drum between a lowered position in which the work supporting surface is substantially horizontal and an upright position in which the axis of the work support perpendicularly intersects the axis of the contact drum medially of its ends; E. power means for imparting work feeding motion to the work support when the arm is in its upright position to feed a workpiece thereon against the contact drum-supported abrasive belt; and F. drive means for rotating the work support about its axis while a workpiece thereon is being fed against the abrasive belt.
 64. The abrading machine of claim 63 wherein said hinge means comprises a hinged frame member mounted to swing about the hinge axis of the hinged arm in unison with said arm; and means to secure said frame member in an upright position; and further characterized in that said power means for imparting work feeding motion to the rotatable work support comprises fluid pressure responsive means reacting between said hinged frame member and said hinged arm.
 65. The abrading machine of claim 64 further characterized by a carriage slidably mounted on the main frame of the machine for translation perpendicularly towards and from the contact drum; wherein the common hinge axis of said hinged arm and hinged frame member is fixed with respect to said carriage so that translation of the carriage provides for adjustment of the distance between the work receiving surface of the rotatable work support and the contact drum to adapt the machine to different sized work; and means for effecting translation of the carriage; and further characterized in that said means for securing said hinged frame member in its upright position comprises latch means on said carriage engageable with said hinged frame member.
 66. The abrading machine of claim 59, wherein said means for bringing the rotatable work support into cooperative relation with said different grit abrasive belt means does so individually and successively, so that a workpiece can be successively abraded by the different grit size belt means without removing it from the rotatable work support.
 67. The abrading machine of claim 66, wherein the different grit size belt means are supported on and driven by a single contact drum; and wherein said means for bringing the work support into cooperative relation individually with the different grit size belt means provides for relative displacement between the work support and the contact drum along a path generally parallel to the axis of the contact drum.
 68. The abrading machine of claim 66, wherein the different grit size belt means are supported by a plurality of contact drums that are disposed in tandem spaced parallel relationship; and wherein said means for bringing the work support into cooperative relation individually with the different grit size belt means provides for relative displacement between the work support and said plurality of contact drums along a path generally normal to the axes of the contact drums.
 69. An abrading machine comprising: A. a turntable mounted to rotate about a fixed axis; B. a plurality of contact drums rotatable about fixed axes normal to the axis of the turntable with their peripheries tangent to a single plane spaced from and generally parallel to the turntable, said contact drums being equispaced from the axis of the turntable; C. an abrasive belt trained over each contact drum, said belts being of different grit size; D. a plurality of rotatable work supports, each adapted to have a workpiece attached thereto; E. means mounting each of the rotatable work supports on the turntable with their axes parallel to that of the turntable and equispaced therefrom a distance such that upon indexed rotation of the turntable the work supports are successively brought into cooperative relation with the contact drums, so that a workpiece on a work support can be successively fed against the different abrasive belts without removing it from the work support to which it is attached; F. said means for mounting the work supports on the turntable comprising arms hinged at one end to the turntable and having the work supports rotatably mounted on the other ends thereof; G. yieldable biasing means reacting between each arm and the turntable to feed the workpiece on its respective work support successively against each of the abrasive belts with a force not exceeding a predetermined magnitude; and H. power means for rotating the work supports while the workpieces thereon are being fed against the abrasive belts.
 70. A surface abrading machine of the type comprising a power driven endless abrasive belt having a stretch thereof supported by a backup member engaging the back side of said belt, a work support member upon which a workpiece is held to be abraded by the belt and which is rotatable on an axis that substantially perpendicularly intersects the zone of contact between the workpiece and the abrasive belt, one of said members being movable toward and from the other to provide for engagement and disengagement between the workpiece and the belt and for relative feeding motion between the belt and the workpiece as abrasion takes place, said machine being characterized by: means for exerting upon said one member a substantially large feed force in the feeding direction by which relative feeding motion of said one member toward the other is effected and which force is imposed upon the engaged surfaces of the workpiece and the belt to cause abrasion of the workpiece, said last named means comprising: A. force producing means arranged to react between said one member and a relatively fixed part of the machine; B. means operatively associated with said force producing means to provide yieldability in its application by which an increase beyond a predetermined magnitude in the resistance the workpiece presents to being abraded is compensated and the feed force maintained constant; C. means for achieving said motion producing means to thereby effect said relative feeding motion; and D. means unaffected by discontinuity in contact between the workpiece and the belt resulting from interruption in the workpiece surface being ground, for controlling the rate at which said relative feeding motion occurs.
 71. The surface abrading machine of claim 70 wherein said force producing means comprises a hydraulic cylinder, one end of which is connected with source of hydraulic pressure and its other end is connected with a hydraulic fluid reservoir during the production of said feed force; and wherein said means for controlling the rate at which said relative feeding motion occurs comprises a flow control valve connected between said other end of the cylinder and the fluid reservoir.
 72. The surface abrading machine of claim 70, wherein said force producing means comprises a screw and nut connection between said one member and said relatively fixed part of the machine; and wherein said means for controlling the rate at which said relative feeding motion occurs comprises means for regulating relative rotation between the screw and nut.
 73. A surface abrading machine of the type comprising an endless abrasive belt trained over a contact drum member, a work support member upon which a workpiece is held to be abraded by the belt and which is rotatable during work performing engagement between the workpiece and the abrasive belt on an axis substantially perpendicular to that of the contact drum member and intermediate the ends thereof, one of said members being movable toward and from the other to provide for engagement and disengagement between the workpiece and the belt and for relative feeding motion between the belt and the workpiece as abrasion takes place, said machine being characterized by: A. hinged arm means having said movable one of said two members mounted thereon; B. rigid frame structure to which said hinged arm means is hingedly connected for swinging movement about an axis substantially parallel with the axis of the contact drum member, to and from a position at which said two members are in cooperative relationship enabling a workpiece held by the work support member and the contact drum member-supported abrasive belt to be brought into engagement; C. force applying means arranged to react between said rigid frame structure and the hinged arm means for effecting work performing engagement between the workpiece and the abrasvie belt; and D. means providing yieldability in said force applying means for cushioning sudden increases in the feed force manifested at the engagement between the workpIece and the abrasive belt and resulting from transient high spots in the workpiece surface and/or hard spots therein.
 74. The surface abrading machine of claim 73, wherein it is the work support that is mounted on the hinged arm means.
 75. The surface abrading machine of claim 73, wherein said means for providing yieldability in said force producing means comprises a closed air chamber having resiliently deformable wall means and containing air under pressure, and through which said force producing means acts.
 76. The abrading machine of claim 73, wherein said force applying means comprises a hydraulic pressure responsive device connected with a pressure source, and wherein said means for providing yieldability in said force producing means comprises control valve means which is sensitive to changes in the force manifested at the engagement between the workpiece and the abrasive belt and operable to govern connection of the hydraulic pressure responsive device with its pressure source.
 77. The abrading machine of claim 19, wherein said endless abrasive belt means comprises a plurality of abrasive belts, each having a stretch thereof supported by a backup member, wherein there are a plurality of work supporting members, each of which meets the definition of the work supporting member set forth in claim 19, and further characterized by: means for selective bringing each work supporting member into cooperative relationship with all of said plurality of abrasive belts, so that a workpiece on any one of said rotatable work supporting members can be successively abraded by the plurality of abrasive belts without removing the same from its rotatable work supporting member.
 78. A surface abrading machine comprising: A. a plurality of power driven endless abrasive belts, each having a stretch thereof supported by a backup member engaging the back side of the belt; B. a plurality of work supporting members, each of which has means for holding a workpiece to be abraded and for rotating the workpiece thereon about an axis that substantially perpendicularly intersects the zone of contact between the workpiece and the endless belt engaged by the workpiece; C. means for selectively bringing said work supporting members into cooperative relationship with said abrasive belts, so that workpieces on said work supporting members can be successively or simultaneously abraded by different abrasvie belts; D. power drive means for effecting relative work feeding motion between a work supporting member and the backup member of the abrasive belt with which said work supporting member has been brought into cooperative relationship; E. means forming a feed rate controlling connection between said members comprising a screw having a force imparting connection with one of said members and a nut threaded on the screw and having a force imparting connection with the other of said members, so that relative work feeding motion between said members is possible only upon relative rotation in one direction between the screw and nut; and F. means for effecting such relative rotation so that the rate of said relative work feeding motion is governed by the rate at which said relative rotation between the screw and nut takes place. 